Role and Regulation of Iron-Sulfur Cluster Biosynthesis Genes in Shigella flexneri Virulence

Abstract

Shigella flexneri, a causative agent of bacterial dysentery, possesses two predicted iron-sulfur cluster biosynthesis systems called Suf and Isc. S. flexneri strains containing deletion mutations in the entire suf operon (UR011) or the iscSUA genes (UR022) were constructed. Both mutants were defective in surviving exposure to oxidative stress. The suf mutant showed growth that was comparable to that of the parental strain in both iron-replete and iron-limiting media; however, the isc mutant showed reduced growth, relative to the parental strain, in both media. Although the suf mutant formed wild-type plaques on Henle cell monolayers, the isc mutant was unable to form plaques on Henle cell monolayers because the strain was noninvasive. Expression from both the suf and isc promoters increased in iron-limiting media and in the presence of hydrogen peroxide. Iron repression of the suf promoter was mediated by Fur, and increased suf expression in iron-limiting media was enhanced by the presence of IscR. Iron repression of the isc promoter was mediated by IscR. Hydrogen peroxide-dependent induction of suf expression, but not isc expression, was mediated by OxyR. Furthermore, IscR was a positive regulator of suf expression in the presence of hydrogen peroxide and a negative regulator of isc expression in the absence of hydrogen peroxide. Expression from the S. flexneri suf and isc promoters increased when Shigella was within Henle cells, and our data suggest that the intracellular signal mediating this increased expression is reduced iron levels.As a facultative intracellular pathogen, Shigella flexneri spends a significant portion of its life cycle within the epithelial cells lining the human colon. Invasion of and intracellular survival/replication of the bacteria within these epithelial cells requires the ability to sense the environment and initiate an appropriate metabolic strategy during infection. Global analysis of Shigella transcription during epithelial cell infection indicated that a variety of metabolic genes, including the suf genes, are precisely regulated when Shigella is intracellular (16,27).The Shigella flexneri suf and isc loci encode predicted ironsulfur (Fe-S) cluster biosynthesis systems. Iron-sulfur clusters are essential for a wide variety of biological processes, including redox reactions, substrate binding and activation, iron storage, protein structure, and regulation of gene expression (11). The S. flexneri isc locus contains iscR, iscS, iscU, iscA, hscB, hscA, and fdx and is highly conserved with the Escherichia coli isc locus. E. coli IscS catalyzes the desulfurization of L-cysteine for the recruitment of S for Fe-S cluster formation (4). IscU and IscA are predicted to form scaffolds for Fe-S cluster assembly based on similarities with Azobacter vinelandii NifU and IscA Nif (1, 11, 13). The chaperones HscB and HscA aid in Isc-mediated Fe-S protein maturation, although the specifics are not entirely clear (for a review, see reference 11). Deletion of the isc locus in E. coli reduced the gro...

IscR Is a Global Regulator Essential for Pathogenesis of Vibrio vulnificus and Induced by Host Cells

“…Accordingly, Fe-S cluster biogenesis and its regulation are crucial for the pathogenesis of Erwinia chrysanthemi and Shigella flexneri, allowing adaptation to hostile host environments (43,44). It is noteworthy that the Pseudomonas aeruginosa IscR also plays a role in survival under H 2 O 2 -and paraquat-induced oxidative stress and in virulence (45).…”

Critical Role of Dispensable Genes inMycoplasma agalactiaeInteraction with Mammalian Cells

“…Serial dilutions of mycoplasma stocks were spotted on blood agar plates, and colony development was observed after 4 to 6 days of incubation at 37°C. (24,32,39,42). The central role played by bacterial SUF machineries in resistance to iron limitation and oxidative stress suggest that the NIF locus might play a similar role in M. agalactiae-host interactions.…”

“…Disrupted CDSs for which a predicted function was assigned correspond to 40% of the total number of CDSs and belong to a broad number of functional categories, often with no obvious correlation between the predicted function and its potential role in M. agalactiae survival under cell culture conditions. Yet several related functions, such as protein folding, iron-sulfur cluster biosynthesis, and DNA repair, have been associated with virulence or stress tolerance in a number of pathogenic bacteria (1,4,24,39,42,43,47). Another 40% of CDSs encode hypothetical products, many of which were shown to display membrane lipoprotein features and/or to have undergone horizontal gene transfer (HGT) with the mycoides cluster (Fig.…”

The unique regulation of iron-sulfur cluster biogenesis in a Gram-positive bacterium

“…The ability of apo-IscR Tp -wt and apo-IscR Tp to bind the promoter region of the suf operon suggests that IscR Tp can function as an Fe/S cluster regulator in this organism, with the apo form involved in the regulation of the suf operon expression, as observed for E. coli. Although such regulators have been found and characterized in a number of Gram-negative bacteria (7,8,(33)(34)(35), the characterization of orthologous proteins from Gram-positive species has not yet been reported. Therefore, T. potens has a unique organization and regulation of Fe/S cluster assembly genes, among Grampositive bacteria.…”